This invention is related to telephone systems and, more particularly, to telephone signal processing systems including a port multiplexer for connecting a plurality of linefinders and first selectors to a telephone signal processor, such as a tone-to-pulse converter.
As described in the above-referenced U.S. patent incorporated herein by reference, as noted above, port multiplexers are electronic circuits adapted to couple a plurality of linefinder/first selector combinations to a signal processor, such as a tone-to-tone pulse converter. When needed, the port multiplexer connects a seized telephone line to the signal processor. The signal processor processes information received from a related linefinder, and transmits processed information, via the port multiplexer, to a related first selector. For example, when a subscriber picks up the handset of a DTMF (dual tone multifrequency) telephone and seizes a linefinder in a system not adapted to transmit DTMF signals, a port multiplexer, if included in such a system, couples the DTMF telephone to an idle tone-to-pulse converter (signal processor). The depression of the push buttons of the DTMF telephone, which cause dual tones to be generated, is detected by the tone-to-pulse converter and converted into a series of rotary dial type pulses. These pulses are then transmitted via the port multiplexer to an associated first selector.
The port multiplexer described in the above-referenced U.S. patent includes a plurality of links that connect linefinder/first selector combinations to a plurality of ports which, in turn, are connected to signal processors. The links are connected between the linefinder/first selector combinations and are sequentially interrogated by an address generator/clock combination. When a link associated with a particular port is seized, the port causes all of the other links associated with it to place false busy status information on the C-leads connected to such other links, whereby related linefinders are prevented from attempting to seize the seized port. Upon termination of signal processing, the port and the port seizing link are released. Further, upon termination of a conversation, even though a port has been seized by another associated link, the conversation related line is released by the production of a WINK signal that interrupts the false busy status information for a short period of time.
While the links described in said U.S. patent have reduced the cost of port multiplexers, they have certain disadvantages. The present invention is directed to overcoming these disadvantages. For example, the links described in said U.S. patent require that the C-lead, not just the tip and ring leads, running between linefinders and first selectors be split. Then, a coupling portion of the link is connected in series with the C-lead. Since the C-lead carries certain information usable by other circuitry, splitting of the C-lead and the insertion of serial components causes undesirable electric circuit problems. For example, it prevents employees from making use of the make-busy switch normally associated with linefinders and first selectors. Thus, re-education of employees is required using this system. In addition, the links described in said U.S. patent have certain other disadvantages. For example, they require the inclusion of a clock and an address generator. Obviously, it would be desirable to eliminate the expense of these items and, thereby, reduce the cost, and improve the reliability, of links.
Therefore it is an object of this invention to provide a new and improved link.
It is a further object of this invention to provide a new and improved link system for linking a plurality of linefinder/first selector combinations to a port.
It is yet another object of this invention to provide a new and improved link arrangement that is more economical and more reliable than prior art links.